Re: 1 nap or 2
For us it happened pretty naturally at around 13.5 months. (DS is 15 MO now) It's nice he goes down for 2-3 hours in the middle of the day and I can catch up on things.
However, occasionally he gets 2 naps I follow his lead. If he get up super early in the AM I know he's going to need a morning nap so I let him have it. Then in the early evening he takes a 30 minute power nap and is g2g until dinner and bedtime.
The days we do 2 naps it's harder all around though, 1 nap is working much better for him.